The present invention generally relates to a driving apparatus and more particularly, to a linear driving arrangement to be used in a copying apparatus or the like for alternately displacing optical mechanisms incorporated in the copying apparatus.
In copying apparatuses of an electrophotographic system, that have a fixed or stationary original document platform are required to make constant, a light path length from surface of an original document to the photosensitive surface of a photoreceptor drum, irrespective of the scanning positions thereof, and therefore, such a copying apparatus is normally provided with a linear driving arrangement. The linear driving arrangement displaces a drum projection optical mechanism and an original document scanning optical mechanism at a speed ratio of 2 to 1 in a scanning direction of the original document (Such a linear driving arrangement for the copying apparatus will be merely referred to as the linear driving arrangement).
A conventional linear driving apparatus will be briefly described with reference to FIG. 5.
In the known linear driving apparatus as shown in FIG. 5, a drum projection optical mechanism DP and an original document scanning optical mechanism OS are coupled to each other through a wire/pulley mechanism F. Mechanism F includes a steel wire W passed around pulleys P1, P2 and P3 and a shaft of a driving motor. The speed is controlled so that the speed ratio thereof becomes to be 2 to 1, while the drum projection optical mechanism DP and the original document scanning optical mechanism OS are further arranged to be displaced at predetermined speed patterns by controlling driving of the motor M connected to said wire/pulley mechanism F.
However, the conventional linear driving apparatus as referred to above has disadvantages. The drum projection optical mechanism DP and the original document scanning optical mechanism OS be connected to and restricted by the steel wire W of the wire/pulley mechanism F, when a variation arising from assembling errors, etc. takes place in an optical path length, positional adjustments for the mechanisms DP and OS can not be readily effected. A very high accuracy is therefore required in the assembly. Similarly, even in the case where a variation with time due to expansion and contraction of the steel wire W, etc. takes place besides the variation by the assembling errors referred to above, it becomes very difficult to make adjustments for bringing an image to be copied into focus. The inconveniences as described above become a serious obstacle for the improvement in the performance of a copying apparatus.